Physiological Behavior of Cork-Oak Acorns (Quercus suber...

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International Journal of Agriculture Innovations and Research

Volume 4, Issue 2, ISSN (Online) 2319-1473

Physiological Behavior of Cork-Oak Acorns (Quercus

suber L.) and Selection of the Best Ecotypes Adapted to

Climate Change

Tlili Nesrine National Institut for Research in Rural

Engineering, Water and Forests

(INRGREF), Rue Hedi Karray, BPn10,

Ariana 2080Tunis. Tunisia.

Emil: [email protected],

Tel: +21693215092

Rachid Loukehaich Université Ibn Tofaïl. Faculté des

Sciences. Laboratoire de Botanique et de

Protection des Plantes. BP 133. Kenitra

(Maroc).

Santiago Ramon Instituto del Corcho, la Madera y el

Carbon Vegetal, Junta de Extremadura,

Poligono Industrial « El Prado », s/n.

Apartado 437, 06800 Merida, Espagne.

Hamrouni Lamia National Institut for Research in Rural Engineering,

Water and Forests (INRGREF), Rue Hedi Karray, BPn10,


Ammari Youssef National Institut for Research in Rural Engineering,

Water and Forests (INRGREF), Rue Hedi Karray, BPn10,


Abstract – Cork oak forests are extremely variable with

regard to their ecological and socio economic conditions.

Therefore, the impacts of climate change on cork oak forests

are likely to be distributed across different bioclimatic zones.

Nevertheless, our understanding of the potential of this

species to cope with climate change is necessary. To explore

this, we grew Cork oak seedlings from acorns collected at

twenty Tunisian populations selected from climatically

contrasting localities and covering an aridity gradient

(Kroumirie and Relicts areas). Acorn size and moisture

content were evaluated as a possible adaptive trait enhancing

stress resistance. Seedling morphological traits (height,

diameter and number of leaves) were analyzed after three

month growing. There were significant correlations among

the considered acorn morphology and seedling traits. Relicts

populations originating from sites with the driest summers

exhibited the highest survival rates. These populations were

characterized by bigger germination rate, suggesting

selection for this trait across sites experiencing drought. Our

findings reveal that Kroumirie populations are not very well

adapted to cope with increasing drought. The physiological

behavior response was more related to the geographical

origin. Seedling traits tolerant to drought might have a high

potential for vegetation recovery in afforestation projects and

restoration programme particularly under water-limited

environments or in degraded areas.

Keywords – Cork Oak, Climatique Change, Kroumirie,

Relicts Areas, Acorn Size, Moisture Content, Morphological

Traits.

I. INTRODUCTION

Cork oak (Quercus suber L.) is one of the most

important forest species growing in mediterranean basin,

because of its distinctive properties. Ecologically it serves

as an environmental protector and stabilising the marginal

areas species [1]. In Tunisia, this genus is distributed from

north to south in the forests belonging to two different

areas (Kroumirie and Relicts areas). In fact, Cork oak

forest provide a wide range of environmental activities,

including biodiversity conservation, soil conservation, fire

prevention resilience to climate change and desertification,

carbon fixation [2].

It displays intermediate to tolerance to drought and high

temperatures, being considered a transitional

species between the high drought tolerant evergreen

oaks [3]. Populations of cork oak become scarce and

scattered going northward due to cold winters and

eastward due to dry conditions [4]. Models predicting

suitable habitat for forest tree species under future climate

change scenarios indicate that the range of Q. Suber could

decrease drastically in southern Tunisia [5]. It could also

extend its distribution northwards and to higher altitudes

benefiting from a potential increase in winter temperatures

[6]. However, those models that predict species

redistribution with climate change largely ignore within-

species genetic variation [7]. In the short term, the

potential of species to respond to these rapid changes will

depend on their phenotypic plasticity as much as intra-

specific genetic variation for adaptive traits [8].

Seed size is one of the most important traits influencing

the early stages of the life cycle of the plant. The

importance of seed size in governing the fitness of

progeny has been supported by extensive empirical

evidence [9] ; several studies have found that larger seeds

help seedlings to endure drought [10]-[11], and promote

germination [12]-[13] , growth and survival [14]. Seed

size can be affected by the original environment, primarily

due to seed sensitivity to resource availability 15]- [16].

In general, growth parameters of seedlings such as height,

diameter, and fresh weight increase as seed size

increases[17]. A positive relationship among acorn size,

seedling height and summer survival has been reported for

other Mediterranean oak species [18]. Several studies have

reported that bigger acorns lead to increased seedling

growth [19] - [22] and higher root/ shoot ratios [23] - [24],

which can improve the seedling performance by

developing and maintaining deep and extensive root

systems accessing water from deep within the soil profile

[25]. Owing to large differences in environmental

conditions among populations, Q. suber presents high

inter-population variation in adaptive traits as a

consequence of adaptation to the climate at the place of

acorns origin and populations from the wettest sites had

Manuscript Processing Details (dd/mm/yyyy) :

Received : 18/08/2015 | Accepted on : 25/08/2015 | Published : 07/09/2015


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the smallest average seed size and the lowest final survival

under the dry conditions [26].

In the near future, it will be important to increase long-

term studies on natural populations in order to understand

plant response to environmental factor fluctuations

including climate change. The present study was designed

to determine the morphologic response of cork oak acorns

(Quercus Suber L.) from 2 climatically and genetically

different provenances (kroumirie and relicts forests) and

selection of the best ecotypes adapted to climate change.

The present study is part of a large programme, which

aims to determine the capacity of Q. suber to cope with

expected climate change and to contribute to the

development of a strategy for the extensive production of

high quality seedlings of this species for reforestation in

the forests of Tunisia. Our specific objectives were (1) to

estimate the influence of acorn size on the response of Q.

suber to local climatic conditions and (2) to identify which

populations would be the most susceptible to the climate

change expected for the region.

II. MATERIALS AND METHODS

II.1. Study area: We selected twenty populations to cover

the main range of climatic conditions of Q. suber

distribution in Tunisia. Two areas were identified: The

Kroumirie and Relicts Areas (Table 1) and (fig.1).

II.2. Acorn collection: Samples of fresh acorns,

morphologically mature, collected at the end of November

2012 (200 per locality).The acorns were reaped directly

from the selected shrubs (acorns of each shrub per each

population were maintained separated) at the time of

natural dispersal.

II.3. Acorn Morphology: After cleaning, acorns are dried

for one week and a morphological study of these acorns

was determined by measuring the size of fruit (Seed

length, width) using a slide gauge and expressed in cm and

by the shapes (oval, rounded,...), the weight was

determined by measuring the average value of the weight

of 20 acorns .

II.3.Moisture Content: The temperature for moisture

measurement was maintained at 130℃±1℃ for two hours.

The moisture content is expressed as follows [26].

( )% 100

PF PSH

PF

−

=

II.4. Acorn sowing and germination: 20 acorns per locality

were sown in a plastic pot (60 × 20 cm). Acorns were

sown at approximately 2-cm depth in the topsoil, and

covered with the respective litters [27]. The pots were kept

outdoors under natural conditions, and watered regularly

to the field capacity. The germination process was carried

out without pretreatments. The germination time was

monitored daily, and the beginning of germination was

considered when the percentage of germination for each

pot was 20% [28]. After germination of 20 seedlings per

each locality were selected for measurements.

Germination rate is appreciated by the average

germination time (TMG), is expressed is as follows:

. /i i

TMG n t N=

ni = number of seeds germinated at time ti,

N = total number of germinated seeds

II.5. Mortality rate (%): is measure of the number of

deaths in a particular population, per the total number of

emerged plants, per unit of time.

II.6. Growth rate of seedlings: The aerial growth

parameters: the length and diameter of the collar of the rod

and the average number of leaves were observed every

week.

II.7. DATA ANALYSIS: The study results were processed

statistically by the analysis of variance using the program

SYSTAT (Version 10,2). Pearson’s correlation coefficient

was determined for different structural parameters.

III. RESULTS

III.1. Acorns Sizes: The morphological study of acorns

indicates the presence of significant differences. There

was a very high correlation between length and acorn

weight (r2 = 0.78). There were no significant intra-

population differences among length and diameter

(p≤0.05) (Table 2).

For the acorn morphology of the considered

populations; the length ranged from 2.13 ±0,47cm to 3.53

± 0,66cm . Diameter ranged from 0.21 ± 0,05mm to 0.82

± 0,05mm. Weight varied from 2.5 ± 0,97g to 10.28 ± 2,25

g (Fig.2). The statistical comparison of values between

different populations showed that acorns differ in terms of

their weight which shown the highest variability (Table 2).

Within each region; there was significant variability in

the acorn morphology. The highest values were observed

in the provenances of JZ (3.2 cm, i.e. 0.82 mm, 10.2g)

where the smallest values in both length (2.91±0.26cm)

and diameter (0.21±0.063 mm) are present in provenance

of Siliana (JS).

In Kroumirie a significant variation between regions

was observed with a highest value in Tbarka (Population

of Asn) (3.53cm, 0.64 mm, 6.24g) and Ain Drahem

(population of MS) [3.53cm; 0.61mm and 6.33g]. The

average minimum value is in Provenances Aslt (Area of

Fernana) (2.13 cm, 0.59 cm,3.53g ). Area of Ain Drahem

et Nefza was in an intermediate position (Fig.2) and

(Table 2).

In addition, the variations in size and weight, there is

also a variation in the shapes of acorns. For the

provenance of JA, acorns are usually oval. BL DF, BM

and Bab are generally rounded or elongated shape. The

population JA, acorns are ovoid. Whereas those of MS,

AZ, JD, JB and Jk are smaller and rounded. F and Js is

stated to have large elongate acorns. (Fig.3). Our results

show that acorns have different sizes and shapes ranging

from spherical rounded to sub-cylindrical aspects.

III.2. Moisture Content: The moisture content presented

significant differences within each provenances .Three

different groups can be distinguished: A first group highly

hydrated (51.3%) with five provenances of relict area, a

second intermediate (47.1%) with seven provenances, and

a third population weakly hydrated (44.1%) corresponding

to the rest of the population (Tab. 3). The moisture content

of acorns collected in the same locality is different.


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III.3. Seed Germination: The seed germination rate of

Cork oak is shown in Table 4. Our results indicated a

significant difference in germination rate (P ≥0.05) among

the different provenances. The germination rate is between

40% and 76%, except for provenances Jbel sarj (3%) and

Ghorgalia (0%).Relict areas present the best germination

rate such as Population of JA (76,66%) and JZ (73%).

III.4. Mortality rate: There were no significant intra-

population differences among germination rate and rate of

mortality (p≤0.05) (table 4). The mortality rate was high in

population of JB (26%) and low in JZ (2,27%) and Bab (

2,63%) where it was 0 % in BL, BLr , SS, JS and JA.

III.5. Seedling growth: Significant increase in diameter,

length and total number of leaves (Fig.4.5.and 6).

Significant differences were found in the stem growth,

diameter and number of leaves in seedlings which

developed from acorns (Tab .2). The values of Seedling

growth show a significant variation between different

populations. Throughout the observation period, the

population JS (relict area) (Fig.4A.5A.and 6A) and Tb

(kroumirie population) (Fig.4C.5C.and 6C) remarkably

distinguished from the other populations by significantly

lower height growth, diameter and number of leaves

(125.2±6.29 mm; 0.85±0.31 mm; 8.5±1.27) (165.2±40.6

mm; 1±0.23 mm; 13.66±3.88) respectively.

Population JA, JB and JZ (Relict populations) seedlings

had the highest diameter (320 ± 21.67mm)

(314±16.74mm) (294±15,06mm) respectively, and

distinguished by the significantly highest number of leaves

JZ(25.33±2.21 ), JB( 22±1.7) and JA (21.83±2.5), while

provenances of Fernana have the lowest number of leaves

(15.11±1.23 mm), diameter (1.32±0.03mm) during the

growth period (Fig. 4D, 6D) (Tab 5). The average

diameters was recorded in Ain Draham (1.24 ± 0.007

mm), Tabarka 1.24 ± 1.33mm and Nefza (1.24 ± 0.07 mm)

(Tab 5).

The Pearson’s correlation analysis underlines a

significant correlation among Acorn size, Moisture

Content and growth parameters between the different

studied cork oaks populations (Tab.2).

IV. DISCUSSION

The significant differences in the seed germination and

size of the considered Quercus acorns seem to be in

relationship with the local conditions [29]. The results of

our research indicate that Q. suber seedlings from the two

areas: Kroumirie and relicts are characterised by different

morphological (morphological include the size) and

physiological traits. This morphological study of acorn

should produce guidelines for the selection of genotypes

that yield fruits with desirable characteristics. A direct

correlation between acorn size and young seedling

survival and a positive correlation of seedling size and

acorn size are reported [30]. Our results confirm these

observations with significant differences in physiological

behaviour of cork-oak acorns in the different populations.

For relict population; the large acorns size (may be

justified by the drier climatic conditions of their original

localities [31, who underlines that large seed size

accelerates germination time and increases germination

rate, seedling survival, and seedling growth. This is what

has been observed in Relict populations JZ , JB and JA

who presented some of these adaptation characteristics ,

the highest acorn size and weight with highly water

content, the high germination capability, the lowest

mortality rate and the highest growth in length, weight

and number of primordial leaves. Relicts populations are

considered the most fertile population that could be

considered as an ecotype of reforestation in the future

[32].

On the contrary, Js ( Area and Siliana) and Tb ( Area of

Nefza ) presented lowest parameters of acorn size ,weight

and water content with the highest mortality rate and

lowest growth parameters. These results indicate that

morphological seedling traits probably driven by the

climate of the localities from which they were originated.

These areas have unfavorable climatic conditions in areas

that are in the limits of Cork oak distribution [32].

In Kroumirie: The small acorns size Asn (Area of

Fernana), can be related to the cold stress, because of the

lowest photosynthetic rates of the cold stressed Quercus

parent plants [33]. In fact, the cold stress inhibits the

activity of sucrose synthesizing enzymes like sucrose

phosphate synthase which has a high sensitivity to low

temperatures [34]. Several authors underline that Acorns

from this provenance had a lower size and volume during

the harvest and so thereafter shorter growth and less robust

over time [35] , they have acquired over the years a great

capacity to mobilize soil water reserves stored during the

winter and to regulate their evapotranspiration[36]-[37].

This new generation is a direct descendant of cork oak

trees located on the south side of the Kroumirie at low

altitude and subjected to continental influences with very

hot and very dry summers. These trees are small and have

low circumference; regarding the altitude of oaks [35].

For Ain Drahem ( population of Bab , AZ and Ms ) ,

Tabrka( population of ASn) and Nefza (Blr ) present

intermediate acorns size which are justified by the

favorable climatic [38]. This suggests that provenances

from bioclimate subhumide, presents a weather conditions

which are favorable for the growth of Cork oak [32] .

In general, growth parameters of seedlings such as

height, diameter, and fresh weight increase as seed size

increases [39]. Large seed size has often been linked to

enhanced seedling survival and regeneration success [40] -

[41, The effect of seed size on seedling performance is

highly variable and depends on environmental conditions

such as drought [42] . Our results indicate that large seeds

of Q. suber from populations can render restoration

programs in the Tunisia forests more successful [43].In

fact, seed size variation is thought to be important for the

establishment of seedlings under field condition [44] , and

larger seeds can improve the establishment of seedlings

under competitive and resource-limiting conditions [45] .

For example, several research found that seedlings from

smaller seeds were better under moderate levels of water

stress [46]; however, under severe water stress seedlings

from large seeds were more tolerant and also found that

larger seeds of Quercus suber from drier populations


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exhibited the highest survival rates under dry conditions

[47]-[48] .

The discriminate Analysis confirms the obtained results

identifying on the basis of the considered acorn and

seedling traits, eight groups and underlining a complete

separation between the region of Silana and Fernana ,

which explains 50% of the total variance, and an

intermediate position of Zaghouana included with nabeul ,

Ain Drahem and Tbarka . Nevertheless, Nefza and

Tbarka are closer to each other , by their similar climatic

and soil conditions (Fig.7) .

Overall our results underline that Q. suber is

characterised by a large variability of acorn and seedling

traits which could be considered for afforestationprojects

and restoration programmes. The knowledge of seed

germination and seedling growth capability in response to

the intensity and duration of water stress in the

Mediterranean Basin is important because water

availability is a limiting factor of prime importance in the

oak regeneration [49] (Trubat et al . 2010).

The early stages of oak population’s seedlings

development are affected differently by changes in soil

water reserves and temperature [35] In general, forest

trees such as oak cork show a phenological variability as

well as morphology, as shown by several provenance tests

[50] -[51]. The variability observed between populations

can depend on two factors: the intra-populational

variability and the inter-populational variability related

both to the effect of the environment and to the genetic

structure of the population [52].

In particular, the large acorns may have a high potential

in resource-limited or degraded areas by their better

germination rate and growth seedlings capability in the

establishment phase, and by the highest capability to

maintain a more stable water-use efficiency which may be

advantageous during the early life stages, particularly

during the first summer drought following planting in

afforestation projects. Physiological knowledge

concerning populations of Q. suber seedlings from

different climate are important to forecast the potential

productivity to increasing drought stress.

V. CONCLUSION

The purpose of this study of acorn morphological and

physiological characteristics was to establish the nature

and range of variation within and between populations.

The results from this study should serve as guidelines for

the selection of the best ecotypes of cork-oak acorns

(Quercus suber L.) adapted to climate change throughout

its distribution range. In this study, The relicts zones are

the best compared to the Kroumirie area. Ecophysiological

behaviour of relict population represents a population

model of type 'resistance model' or type 'stabilisation

model' (Ramírez et.2010). In the near future, it will be

important to increase long-term studies on natural

populations in order to understand plant response to

environmental factor fluctuations including climate

change.

ACKNOWLEDGEMENTS

We would like to thank INRGREF ( National Institut for

Research in Rural Engineering, Water and Forests) and

IPROCOR- CICYTEX( Centro de Investigación del

Corcho, la Madera y el Carbón Vegetal del Centro de

Investigaciones Científicas y Tecnológicas de

Extremadura). I wish to thank Prof. Dr. Ksontini

Mustupha for his support during the seed collection. We

are grateful to Abdstar Salh, technician of INRGREF, that

collaborated in the setting up of the cork oak field trials.

We would like to thank to Ernesto Trias, administrative in

IPROCOR, for his valuable suggestions.

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248



Table 1: Cork oak populations and some geographical and climatic characteristics of the study localities.

Subdivision Pop Altiude

Geographic Characteristics Climatic Characteristics

Latitude

Longitude Annual mean

Temperature

°C

Annual mean

precipitation

(mm)

Bioclimatic

floor

kroumirie

area

Ghardimaou

Fernana

Fernana

Sejnane

Tbarka

Tbarka

Tbarka

Nefza

Nefza

Nefza

Nefza

AinDrahem

Ain Drahem

Ain Drahem

AinDrahem

Ain Drahem

Ast

F

SS

BL

W

Asn

JK

BLr

GH

JD

Tb

AZ

BM

Bab

DF

MS

836

793

375

158

151

868

375

270

166

477

353

720

498

660

862

552

36°52’52‘’ N

36°50’21’’ N

36°64’76’’ N

37°07’74’’ N

36°99’57’’ N

36°81’43’’ N

36°93’93’’ N

37°02’01’’N

37°07’28’’ N

36°68’84’’ N

36°89’52’’ N

36°78’77’’ N

36°74’98’’ N

36°78’26’’ N

36°78’86’’ N

36°76’31’’ N

8°33’05’’E

8°30’68’’E

8°66’34’E

9°16’46’’E

8°93’62’’E

8°74’12’’E

8°95’01’’E

9°08’07’’E

9,05’13’’E

8°62’21’’E

9°06’73’’E

8°88’54’’E

8°73’13’’E

8°65’75’’E

8°74’19’’E

8°79’02’’E

17,7

16

22

18

18,1

19

18

16

18

16,11

19

15

16

16,2

15,5

15,9

580

370

351

741

865

816

829

724

657

732

551

835

1020

1093

1200

963

Semiarid

Semiarid

Semiarid

Humid

Humid

Humid

Humid

Humid

Humid

Humid

Humid

Humid

Humid

Humid

Humid

Humid

Relicts

areas

Sliman

Grombalia

Zaghouan

Siliana

JA

JB

JZ

JS

466

364

939

709

36°85’16’’ N

36°50’78’’ N

35°92’45’’ N

36°47’70’’ N

10°78’18’’E

10°44’71’’E

9°51’37’’E

10°31’68’’E

17,8

17,7

16,1

17,9

444

459

483

432

Semiaird

Semidarid

Semiarid

Semiarid

Table 2: Results of the Pearson’s correlation analysis among the considered seed variables. [Bold type indicate

significant correlation (P < 0.05)].

Table 3: Moisture content variation. Groups Populations Moisture Cntent (%)

I

Jzid (a)

Blr (a)

JA (a)

AZ (ab)

JB (ab)

Moyenne

53,78±6,68

52,62±4,99

51,92±7,38

50,35± 7,87

49,63±6,63

51,66±1,68

II JK (b)

Wech(b)

MS (c)

Asn (c)

F (c )

JS (c)

SS (cd )

Moyenne

48,77±7,56

47,77±4,35

46,45±8,98

46,91±10,35

46,65±10,63

46,11±8,61

45,78±11,03

46,92±1,03

III GH (e)

Jdis (e)

Tb (e)

DF (e)

BM (ef)

Aslt(ef)

BL (ef)

Bab(ef)

Moyenne

44,94±7,56

44,36± 8,31

43,75±11,88

43,69±6,22

42,60±10,63

42,52±6,42

41,72±12,03

42,52 ±6,42

43,22±1,22

For populations, a significant difference (P <0.05) is

observed when the letters are different.

Table 4: Germination rates (%) and rate of mortality % of

Quercus Cork acorns. Provenances Germination rates

(%)

Rates of

mortality (%)

Ast

F

SS

BL

W

Asn

JK

BLr

GH

JD

Tb

AZ

BM

Bab

DF

MS

JA

JB

JZ

JS

63,33

60

40

13,33

25

45

43,33

51,66

0

43,33

40

38,33

60

63,66

28,33

70

76,66

70

73,33

5

7,89

5,55

0

0

6,66

3,70

3,84

0

-

7,69

8,33

13,04

5,55

2,63

17,64

4,76

0

26,19

2,27

0

Width Weight Moisture

Content

Seed

Germination

Growth In

Length

Growth In

Diameter

Number of

Leaves

Length 0,04204601 0,78194235 0,72090648 0,16790066 0,20466704 0,12804738 0,18663463

width 0,17891461 0,04491937 0,19659097 0,20155254 0,07714053 0,22219995

Weight 0,94670071 0,31949801 0,26059292 0,29248391 0,29803442

Moisture Content 0,34823252 0,33832199 0,32503486 0,37009385

Seed Germination 0,72885231 0,62452456 0,68123401

Growth in length 0,84973257 0,85064085

Growth in diameter 0,86283713


249



Table 5: Evolution of Seedling Growth by region.

Region Length(mm) Diameter (mm) Number of leaves

Kroumirie

Area

Ain Drahem 240,8±4,79 1,24±1,33 16,70±2,1

Nefza 258,33±3,21 1,24±0,07 17,88± 2,23

Bizerte 280±0,57 1,4±0,08 19,66±1,6

Tbarka 264±0,30 1,63±1,82 18,27±3,3

Fernana 274,66±0,29 1,32±0,03 15,11±1,23

Relicts Areas Nabeul 317±0,09 1,49±0,15 21,99±2,11

Zaghouana 294±0,22 1,78±0, 64 25,33±2,09

Siliana 125,2±0,26 0,85±0,063 8,5±1,27

Fig.1. Map showing the locations of acorn collection sites in Tunisia : Kroumirie (a)

and Relict (b ) populations.

Fig.2. Acorn length (L), acorn width (W) and acorn fresh weight (Wf ) from the considered populations.

(a)

(b)


250



Elongated acorns

Acorns sub -rounded

Large Acorns

Rounded Acorns

Fig.3. Variation of shapes acorns of cork oak (Quercus Suber. L).

Fig.4. Growth in length of cork oak populations :

(A)= Relicts areas, kroumirie area: [(B) Ain Drahem , (C) Tbarka and Nefza , (D) Fernana].


251



Fig.5. Growth in diameter of cork oak populations: (A)= Relicts areas, kroumirie area: [(B) Ain Drahem , (C) Tbarka

and Nefza , (D) Fernana] .


252



Fig.6. Growth in number of leaves of cork oak populations:

(A)= Relicts areas, kroumirie area: [(B) Ain Drahem , (C) Tbarka and Nefza , (D) Fernana] .

Canonical Scores Plot

Fig.7. Analysis of total base composition of Cork Oak L. Results of the linear discriminant analysis along the first and

second discriminant axes [Factor (1) and Factor(2)]

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